1. Field of the Invention
The present invention relates to braking force control apparatus and method for an automotive vehicle which enable the vehicle to perform a stable cornering.
2. Description of the Related Art
A Japanese Patent Application First Publication (Tokkai) Heisei 2-171373 published on Jul. 3, 1990 exemplifies a first previously proposed vehicular braking force control apparatus which has a purpose of securing a stability of a vehicular cornering. In this first previously proposed braking force control apparatus, as a traction control, with an acceleration slip of a driven wheel detected, the acceleration slip is not merely suppressed but a vehicular cornering state variable is detected from a driving state of the vehicle, in a case where the detected cornering state variable approaches to a predetermined braking operation threshold value which has a predetermined margin for a cornering limit state variable up to which the vehicle is enabled to travel stably, a target deceleration required to maintain a stable cornering of the vehicle is calculated, and a braking force to achieve the target deceleration is provided for the vehicle.
Thus, as a result of the control in such a way that the vehicle is controlled so as not to exceed the limit cornering state variable up to which the vehicle is stably enabled to corner during the vehicular cornering irrespective of an intention of the driver, quick and appropriate vehicular deceleration is carried out so that the vehicular stability can be secured even if the vehicle enters a sharp corner having a small radius of curvature at an excessively high speed contrary to the driver's expectation. However, for example, a liquid pressure brake apparatus which provides a braking force for each of road wheels is supposed as an actuator which provides the braking force for the vehicle. In, so-called, a pump-up system which includes a liquid pressure brake actuator in which a motor pump is equipped as a pressure generating source of the liquid pressure brake apparatus, a time is required from a time at which the braking force control is started to be operated to a time at which the motor pump is operated and a brake liquid pressure is raised within each of wheel cylinders. Therefore, an initial responsive characteristic becomes delayed. To solve this problem of the delayed initial responsive characteristic, a second previously proposed vehicular braking force control apparatus as disclosed in a Japanese Patent Application First Publication (Tokkai) No. 2001-63541 published on Mar. 13, 2001 has been proposed in which a technique of a pre-pressure application is used.